Concept:Tayammum is a dry purification method that replaces wudu when water is not available.Explanation:Water is normally required for wudu before prayer.Islam allows tayammum when there is no water or when obtaining water is extremely difficult.Clean earth or dust is used to wipe the face and hands in this situation.This permission is based on the intention to make prayer easier during hardship.It is not performed merely because a person is in a hurry or has missed the prayer time.Answer:Option C: Access to water is very difficult.